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Physicians tend to form informal networks in which they develop ties and connections with other physicians through sharing care of multiple patients, researchers have found.

Note physicians with ties to each other were far more likely to be based at the same hospital.

Physicians tend to form informal networks in which they develop ties and connections with other physicians through sharing care of multiple patients, researchers found.

In a nationwide analysis using social network analysis techniques, the number of other clinicians an individual physician was connected to, through sharing of patients, was 27.3 per 100 Medicare recipients, according to Bruce E. Landon, MD, and colleagues from Harvard University.

In many areas of the country, being based at the same hospital was a strong predictor of physicians having patient-based ties to their fellow clinicians, with an adjusted rate ratio of 0.12 (95% CI 0.12 to 0.12, P<0.001), the researchers wrote in the July 18 Journal of the American Medical Association.

"The potential influence of informal networks of physicians on decision making has been understudied despite the potential importance of these networks in day-to-day practice," Landon's group observed.

In an editorial comment, Valerie A. Lewis, PhD, and Elliott S. Fisher, MD, of Dartmouth Medical School in Hanover, N.H., explained the importance of understanding these relationships and between-physician ties.

"Because many of the policy changes now under way in the U.S. healthcare system are intended to foster collaboration and improve coordination among physicians, understanding physician social networks will be important," Lewis and Fisher wrote.

To explore the characteristics of these informal networks among physicians, Landon's group analyzed Medicare claims for 2006 from 51 geographic areas around the country, identifying each pair of physicians who were connected through individual patients.

Ties among physicians were weighted according to the number of patients they shared, and a relative threshold of 20% was chosen as representing the strongest ties.

The analysis included 4,586,044 Medicare recipients and 68,288 physicians.

Among the physicians, mean age was 49 and 80% were men.

For the patients, the mean age was 71 and 40% were men.

In the individual geographic areas, there were considerable variations in numbers of physicians, ranging from 135 in Minot, N.D., with 1,568 ties among the individual clinicians, to 8,197 in Boston, with 392,582 ties through shared patients.

The degree of connectedness was much greater in Boston, where the average clinician had a connection through patient sharing with 51.4 other clinicians, compared with 11.7 in the North Dakota region.

Overall, 96% of pairs of connected physicians were based in the same hospital, compared with 69.2% of those considered unconnected. However, this varied according to location.

For example, in Albuquerque, the main hospitals are distant from one another, and physicians were more likely to have ties to others within the same hospital. In contrast, in Minneapolis/St. Paul, the large hospitals are geographically clustered, and fewer ties within the same hospital were found.

Physical proximity also was important, with connected physicians having a mean distance from one another of 21.1 km (13.1 miles) compared with 38.7 km (24 miles) for those considered unconnected (P<0.001).

Among physician characteristics that were associated with connectedness were gender, with males having ties with other males (65.1% versus 54.6%, rate ratio 1.32, P<0.001) and medical specialists being more connected than surgical ones.

Patient populations also tended to be similar among clinicians with ties to one another.

Connected physicians had similar proportions of black patients, differing by only 8.8 percentage points, whereas there was 14 percentage point difference for those without connections, the researchers reported.

Connected physicians not only had similar racial makeup in their patient populations, but their patient comorbidities also were similar. "Physicians thus tend to cluster together along attributes that characterize their own backgrounds and the clinical circumstances of their patients," the researchers wrote.

Limitations of these analyses included reliance on Medicare data, so findings may differ with younger patient groups.

In addition, data from only one year were examined, and the broader adoption of electronic medical records in recent years may have influenced physician ties.

In their comment, Lewis and Fisher explained that enhancing the ties among physicians will be central to reform of the U.S. healthcare system.

"The explicit intent is to encourage collaboration among physicians, other clinicians, and hospitals to improve care not only for individual patients (by coordinating the care delivered by multiple clinicians across space and time) but also for populations (by developing shared clinical pathways that ensure the best possible care for patients with specific health problems)," they wrote.

Several of the authors have ties to Activate Networks, which applies some of the concepts explored in the study.

Other disclosures included support from the National Institutes of Health, and consultancy to Daller Shaller Consulting and MedNetworks.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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